The present invention relates generally to integrated circuit designs, and more particularly to methods and systems for improving a sense margin when reading data from memory cells.
Magneto-resistive random access memory (MRAM) that uses magnetic components is becoming one of the most popular technologies for storing data bits. Instead of using electrical charges, as typically used in memory modules such as dynamic random access memory (DRAM) and static random access memory (SRAM), MRAM uses magnetic charges to store data bits. Unlike DRAM and SRAM, MRAM is a non-volatile device that does not require a constant electrical power to retain stored information. MRAM is therefore especially appealing in portable applications, such as mobile computer devices, that typically have a limited power supply.
A MRAM cell stores a data bit by being programmed in a high or low resistance state. Conventionally, methods for reading MRAM cells use only one sense amplifier to compare the output current from a predetermined MRAM cell with the reference current from a pair of reference MRAM cells. One of the reference MRAM cells is programmed to have a high resistance while the other is programmed to have a low resistance. A predefined voltage will apply to the predetermined MRAM cell to generate the output current, and the reference MRAM cells to generate the reference currents. The reference currents are averaged and then compared with the output current. If the output current is greater than the average reference current, the sense amplifier will output a logic “1” (or logic “0”) signal.
This conventional method provides a rather limited sense margin when comparing the output current with the reference current. If an output current significantly deviates from its normal state, a sensing failure may occur. Thus, improved designs that increase the sense margin are therefore desired.